Liquid crystal display device

ABSTRACT

In a liquid crystal display (LCD) device having a touch panel function, power consumption is reduced in the standby state. The display section is divided into blocks each of which is formed of a plurality of display lines. The counter electrode is disposed for each block. A driving circuit selectively supplies, to the counter electrode of each block, the voltage used for the liquid crystal display and the voltage used for the touch panel scanning. The driving circuit has a source amplifier that supplies the video voltages to the video lines. The driving circuit reduces the current in the source amplifier, such that the current is lower than current at the time of a normal operation, to lower the power consumption, and stops the operation of the source amplifier and supplies the GND voltage to the video lines to further lower the power consumption.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/122,061 filed on Sep. 5, 2018, which, in turn, is a continuation ofU.S. patent application Ser. No. 15/805,204 (now U.S. Pat. No.10,096,295) filed on Nov. 7, 2017, which, in turn, is a continuation ofU.S. patent application Ser. No. 14/706,703 (now U.S. Pat. No.9,847,071) filed on May 7, 2015, which, in turn, is a continuation ofU.S. patent application Ser. No. 13/851,229 (now U.S. Pat. No.9,082,367) filed on Mar. 27, 2013. Further, this application claimspriority from Japanese application JP2012-123908 filed on May 31, 2012,the entire contents of which are hereby incorporated by reference intothis application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid crystal display device, andparticularly to a technique that is effective applied to an in-cellliquid crystal display device having a built-in touch panel.

2. Description of the Related Art

There are display devices having a device (hereinafter also referred toas a touch sensor or a touch panel) that inputs information byperforming a touch operation (contact pressure operation, andhereinafter simply referred to as touch) on a display screen with auser's finger, a pen, or the like. The display devices are used inmobile electronics such as PDAs and portable terminals, various kinds ofhome appliances, automated teller machines, and the like.

As such a touch panel, an electrostatic capacitance type touch paneldetecting a change in the capacitance of the touched portion is known.

Well known as the electrostatic capacitance type touch panel is aso-called in-cell liquid crystal display device of which a liquidcrystal display panel has a touch panel function as disclosed inJP2009-258182A.

In the in-cell touch panel, the counter electrode (also referred to as acommon electrode (CT)), which is formed on a first substrate (alsoreferred to as a TFT substrate) constituting the liquid crystal displaypanel, is divided, and is also used to serve as scanning electrodes ofthe touch panel.

SUMMARY OF THE INVENTION

In the in-cell liquid crystal display device having a built-in touchpanel, it is possible to reduce the number of components by forming aliquid crystal display panel driver IC, which drives the liquid crystaldisplay panel, and a touch panel driver IC, which detects a touchposition, as a common driver.

However, in the in-cell liquid crystal display device having thebuilt-in touch panel, when the liquid crystal display panel driver ICand the touch panel driver IC are formed as a common driver, a voltagefor driving the touch panel and a voltage for driving the liquid crystaldisplay panel are made to be common.

The liquid crystal display device detects the touch position on thetouch panel even in a standby state. Hence, there is a problem in that,in the standby state, the liquid crystal display device is in a displayoff state in which “black” is displayed on the liquid crystal displaypanel but nevertheless it is difficult to reduce power consumption inthe liquid crystal display device.

The invention has been made to solve the problem in the related art, andit is an object of the invention to provide a technique, which iscapable of reducing power consumption in the liquid crystal displaydevice at the time when the display is off, which displays “black” onthe liquid crystal display panel in the standby state, for the in-cellliquid crystal display device having the touch panel function.

The above object, other objects, and new features of the invention areclarified by description and accompanying drawings of the presentspecification.

Typical embodiments of the invention disclosed in the presentapplication will be briefly described as follows.

(1) According to a first aspect of the invention, there is provided aliquid crystal display device including a liquid crystal display panelthat has a first substrate, a second substrate, and a liquid crystalsandwiched between the first substrate and the second substrate, inwhich there is provided a display section formed of a plurality ofpixels arranged in matrix, wherein the second substrate has detectionelectrodes of a touch panel, wherein the first substrate has pluralityof video lines which supply video voltages to the respective pixels,wherein each pixel has a pixel electrode and a counter electrode,wherein the display section is divided into a plurality of blocks eachof which is formed of the pixels disposed on a plurality of displaylines adjacent to one another, wherein the counter electrode is anelectrode common to the pixels in each block, wherein the counterelectrode of each block also functions as a scanning electrode of thetouch panel, wherein the liquid crystal display device has a drivingcircuit which supplies the video voltages to the respective video linesand supplies a counter voltage and a touch panel scanning voltage to thecounter electrodes of the respective blocks, wherein the driving circuithas a source amplifier circuit which supplies the video voltages to thevideo lines, wherein the source amplifier circuit has a currentadjustment circuit capable of adjusting current flowing in the sourceamplifier circuit itself, and wherein the driving circuit causes thecurrent adjustment circuit to reduce the current, which flows in thesource amplifier circuit, such that the current is lower than current,which flows in the source amplifier circuit at the time of a normaloperation, in a first low power consumption mode for achieving lowerpower consumption than the normal operation, and causes the currentadjustment circuit to stop an operation of the source amplifier circuitand supply a GND voltage to the video lines in a second low powerconsumption mode for achieving lower power consumption than the firstlow power consumption mode.

(2) According to a second aspect of the invention, there is provided aliquid crystal display device including a liquid crystal display panelthat has a first substrate, a second substrate, and a liquid crystalsandwiched between the first substrate and the second substrate, inwhich there is provided a display section formed of a plurality ofpixels arranged in matrix, wherein the second substrate has detectionelectrodes of a touch panel, wherein each pixel has a pixel electrodeand a counter electrode, wherein the display section is divided into aplurality of blocks each of which is formed of the pixels disposed on aplurality of display lines adjacent to one another, wherein the counterelectrode is an electrode common to the pixels in each block, whereinthe counter electrode of each block also functions as a scanningelectrode of the touch panel, wherein the liquid crystal display devicehas a driving circuit which supplies a counter voltage and a touch panelscanning voltage to the counter electrodes of the respective blocks,wherein the driving circuit has a common amplifier circuit whichsupplies the counter voltage to the counter electrodes, wherein thecommon amplifier circuit has a current adjustment circuit capable ofadjusting current flowing in the common amplifier circuit itself, andwherein the driving circuit causes the current adjustment circuit tostop an operation of the common amplifier circuit and supply a GNDvoltage to the counter electrodes in a low power consumption mode forachieving lower power consumption than a normal operation.

(3) According to a third aspect of the invention, there is provided aliquid crystal display device including a liquid crystal display panelthat has a first substrate, second substrate, and a liquid crystalsandwiched between the first substrate and the second substrate, inwhich there is provided a display section formed of a plurality ofpixels arranged in matrix, wherein the second substrate has detectionelectrodes of a touch panel, wherein each pixel has pixel electrode anda counter electrode, wherein the display section is divided into aplurality of blocks each of which is formed of the pixels disposed on aplurality of display lines adjacent to one another, wherein the counterelectrode is an electrode common to the pixels in each block, whereinthe counter electrode of each block also functions as a scanningelectrode of the touch panel, wherein the liquid crystal display devicehas a driving circuit which supplies a counter voltage and a touch panelscanning voltage to the counter electrodes of the respective blocks,wherein the driving circuit has a gradation voltage generation circuitwhich generates a plurality of gradation voltages, wherein the gradationvoltage generation circuit has a plurality of amplifier circuits whichoutput the plurality of gradation voltages, wherein each amplifiercircuit has a current adjustment circuit capable of adjusting currentflowing in the amplifier circuit itself, and wherein the driving circuitcauses the current adjustment circuit of a middle amplifier circuitother than a top amplifier circuit, which outputs a highest gradationvoltage, and a bottom amplifier circuit, which outputs a lowestgradation voltage, among the plurality of amplifier circuits, to stop anoperation of the corresponding middle amplifier circuit, in a first lowpower consumption mode for achieving lower power consumption than anormal operation, causes the current adjustment circuit of the middleamplifier circuit to stop the operation of the corresponding middleamplifier circuit and causes the current adjustment circuits of the topamplifier circuit and the bottom amplifier circuit to reduce current,which flows in the top amplifier circuit and the bottom amplifiercircuit, such that the current is lower than current, which flows in theamplifier circuit at the time of the normal operation, in a second lowpower consumption mode for achieving lower power consumption than thefirst low power consumption mode, and causes the current adjustmentcircuits of the respective amplifier circuits, which output theplurality of gradation voltages, to stop operations of the respectiveamplifier circuits and supply a GND voltage as the lowest gradationvoltage, in a third low power consumption mode for achieving lower powerconsumption than the second low power consumption mode.

(4) According to a fourth aspect of the invention, there is provided aliquid crystal display device including a liquid crystal display panelthat has a first substrate, a second substrate, and a liquid crystalsandwiched between the first substrate and the second substrate, inwhich there is provided a display section formed of a plurality ofpixels arranged in matrix, wherein the second substrate has detectionelectrodes of a touch panel, wherein the first substrate has a pluralityof scanning lines which supply a selection scanning voltage VGH and anon-selection scanning voltage VGL to the respective pixels, whereineach pixel has a pixel electrode and a counter electrode, wherein thedisplay section is divided into a plurality of blocks each of which isformed of the pixels disposed on a plurality of display lines adjacentto one another, wherein the counter electrode is an electrode common tothe pixels in each block, wherein the counter electrode of each blockalso functions as a scanning electrode of the touch panel, wherein thecorresponding liquid crystal display device has a driving circuit whichoutputs the VGH and the VGL and supplies a counter voltage and a touchpanel scanning voltage to the counter electrodes of the respectiveblocks, and wherein the driving circuit has a charge-pump VGH/VGLgeneration circuit which generates the VGH and the VGL, and sets anON/OFF period of a switching circuit in the VGH/VGL generation circuitsuch that the ON/OFF period is longer than an ON/OFF period at the timeof a normal operation, in a low power consumption mode for achievinglower power consumption than the normal operation.

(5) According to a fifth aspect of the invention, there is provided aliquid crystal display device including a liquid crystal display panelthat has a first substrate, a second substrate, and a liquid crystalsandwiched between the first substrate and the second substrate, inwhich there is provided a display section formed of a plurality ofpixels arranged in matrix, wherein the second substrate has detectionelectrodes of a touch panel, wherein the first substrate has a pluralityof video lines which supply video voltages to the respective pixels,wherein each pixel has a pixel electrode and a counter electrode,wherein the display section is divided into a plurality of blocks eachof which is formed of the pixels disposed on a plurality of displaylines adjacent to one another, wherein the counter electrode is anelectrode common to the pixels in each block, wherein the counterelectrode of each block also functions as a scanning electrode of thetouch panel, wherein the liquid crystal display device has a drivingcircuit which supplies the video voltages to the respective video linesand supplies a counter voltage and a touch panel scanning voltage to thecounter electrodes of the respective blocks, wherein the driving circuithas a source amplifier circuit which supplies the video voltages to thevideo lines, and a VSP generation circuit, which supplies a highpotential voltage VSP to the source amplifier circuit, and a VSNgeneration circuit which supplies a low potential voltage VSN to thesource amplifier circuit, wherein the VSP generation circuit and the VSNgeneration circuit are switching-regulator-type step-up circuits, andwherein the driving circuit reduces switching frequencies of the VSPgeneration circuit and the VSN generation circuit, in a first low powerconsumption mode for achieving lower power consumption than the normaloperation, and reduces the switching frequency of the VSP generationcircuit and stops an operation of the VSN generation circuit, in asecond low power consumption mode for achieving lower power consumptionthan the first low power consumption mode.

The typical effects, which can be obtained by the invention disclosed inthe present application, will be briefly described as follows.

According to the liquid crystal display device having the touch panelfunction of the invention, it is possible to reduce power consumption inthe liquid crystal display device at the time when the display is offwhich displays “black” on the liquid crystal display panel in thestandby state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view illustrating a schematicconfiguration of a touch-panel-attached liquid crystal display deviceaccording to an example of the related art.

FIG. 2 is a top plan view illustrating an electrode configuration of thetouch panel shown in FIG. 1.

FIG. 3 is a cross-sectional view illustrating a cross-section structureof the touch panel shown in FIG. 1.

FIG. 4 is an exploded perspective view illustrating a schematicconfiguration of a touch-panel-built-in liquid crystal display device.

FIG. 5 is a diagram illustrating a counter electrode and detectionelectrodes in the touch-panel-built-in liquid crystal display deviceshown in FIG. 4.

FIG. 6 is a schematic cross-sectional view illustrating, in an enlargedmanner, a part of the cross section of a display section in thetouch-panel-built-in liquid crystal display device shown in FIG. 4.

FIG. 7 is a top plan view illustrating an example of the counterelectrode divided into a plurality of blocks in the liquid crystaldisplay device according to an example of the invention.

FIG. 8 is a top plan view illustrating a method of driving the counterelectrode divided into the plurality of blocks in the liquid crystaldisplay device according to another example of the invention.

FIG. 9 is a block diagram illustrating an exemplary configuration of thecounter electrode selection circuit shown in FIG. 8.

FIG. 10 is a circuit diagram illustrating an exemplary circuitconfiguration of selection circuits shown in FIG. 9.

FIG. 11 is a circuit diagram illustrating an exemplary circuitconfiguration of the address decoder circuit shown in FIG. 9.

FIG. 12 is a diagram illustrating a driving waveform at the time ofpixel writing and at the time of touch panel detection in thetouch-panel-built-in liquid crystal display device.

FIG. 13 is a diagram illustrating the timing of the pixel writing andthe timing of the touch panel detection in the touch-panel-built-inliquid crystal display device.

FIG. 14 is a diagram illustrating a circuit configuration of a liquidcrystal driver IC according to an example of the invention.

FIG. 15A is a diagram illustrating main liquid crystal driving voltagesat the time of normal display of the liquid crystal display deviceaccording to the example of the invention.

FIG. 15B is a diagram illustrating main liquid crystal driving voltagesat the time of “black” display of the liquid crystal display deviceaccording to the example of the invention.

FIG. 16 is a diagram illustrating an electrode shape of the touch panelof the liquid crystal display device according to the example of theinvention.

FIGS. 17A and 17B are diagrams illustrating touch panel scanningoperations according to the example of the invention.

FIG. 18 is a system state transition diagram of the liquid crystaldisplay device according to the example of the invention.

FIG. 19 is a diagram illustrating a circuit configuration of a sourceamplifier circuit according to the example of the invention.

FIG. 20 is a diagram illustrating a circuit configuration of a commonamplifies circuit according to the example of the invention.

FIG. 21 is a diagram illustrating a circuit configuration of a gradationvoltage generation circuit according to the example of the invention.

FIG. 22 is a diagram illustrating a circuit configuration of a VGH/VGLgeneration circuit according to the example of the invention.

FIG. 23 is a diagram illustrating a circuit configuration of a VSP/VSNgeneration circuit according to the example of the invention.

FIG. 24 is an explanatory diagram illustrating combinations of variouskinds of adjustment circuit states for achieving lower power consumptionin the standby state in the liquid crystal display device according tothe example of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, examples of the invention will be described in detail withreference to the accompanying drawings.

It should be noted that, in overall diagrams for describing theexamples, the components having the same function are represented by thesame reference numerals and signs, and the repeated description will beomitted. Further, the following examples do not limit interpretation ofclaims of the invention.

FIG. 1 is an exploded perspective view illustrating a schematicconfiguration of a touch-panel-attached liquid crystal display deviceaccording to an example of the related art. FIG. 2 is a top plan viewillustrating an electrode configuration of the touch panel shown inFIG. 1. FIG. 3 is a cross-sectional view illustrating a cross-sectionstructure of the touch panel shown in FIG. 1.

Generally, as shown in FIG. 2, the touch panel has scanning electrodes(TX) and detection electrodes (RX) for detecting capacitances. In thedrawing, for example, the number of the scanning electrodes (TX) isthree (TX1 to TX3), and the number of the detection electrodes (RX) istwo (RX1, RX2), but the number of electrodes is not limited to this.

Further, as shown in FIGS. 1 and 3, the touch panel includes: a touchpanel substrate 41; the scanning electrodes (TX) and the detectionelectrodes (RX) formed on the touch panel substrate 41; an interlayerinsulation film 42 formed on the scanning electrodes (TX) and thedetection electrodes (RX); connection portions (STX) that are formed onthe interlayer insulation film 42 and electrically connect the scanningelectrodes (TX); a passivation film 43 formed on the connection portion(STX); a front window (or, protection film) 44 disposed on thepassivation film 43; and a transparent electrode 45 that serves as ashield formed of for example an ITO (Indium Tin Oxide) film on theliquid crystal display panel side of the touch panel substrate 41.

In the touch panel of the related art, a touch panel control IC (DRT)performs pulse driving of the scanning electrodes (TX) with a voltage ofabout 5V to 10V, and the touch panel control IC (DRT) detects changes inthe voltages of the detection electrodes (RX), thereby detecting thetouch position. That is, the capacitance value between the scanningelectrode (TX) and the detection electrode (RX) is changed by a fingeror the like, the voltage, which is detected by the detection electrode(RX) when the scanning electrode (TX) is pulse-driven, is changed, andthe voltage of the detection electrode (RX) is measured, whereby thetouch position is detected.

The touch panel is provided on the front surface of the liquid crystaldisplay panel. Accordingly, in order for a user to view the image whichis displayed on the liquid crystal display panel, it is necessary totransmit the display image through the touch panel. Hence, it ispreferable that the touch panel have a high optical transmittance.

The liquid crystal display panel includes, as shown in FIG. 1: a firstsubstrate (SUB1; hereinafter referred to as a TFT substrate); a secondsubstrate (SUB2; hereinafter referred to as a CF substrate); and aliquid crystal (not shown in the drawing) that is sandwiched between theTFT substrate (SUB1) and the CF substrate (SUB2).

Further, the TFT substrate (SUB1) has a larger area than the CFsubstrate (SUB2). Thus, in the region in which the TFT substrate (SUB1)is not opposed to the CF substrate (SUB2), a liquid crystal driver IC(DRV) is mounted. Furthermore, in the peripheral portion of one side ofthe corresponding region, a main flexible wiring substrate (MFPC) ismounted.

In addition, in FIG. 1, the reference sign “CT” represents a counterelectrode (also referred to as a common electrode), “TFPC” represents aflexible wiring substrate for touch panel, “CD” represents a back-sidetransparent conductive film, “52” represents a connection member, and“53” represents a flexible wiring substrate for connection.

In the IPS liquid crystal display panel, contrary to the TN liquidcrystal display panel or the VA liquid crystal display panel, there isno counter electrode (CT) on the substrate on which the color filtersare provided. Hence, it is necessary to reduce display noise. For thisreason, a back-side transparent conductive film (CD) formed of atransparent conductive film such as ITO is formed on the substrate onwhich the color filters are provided.

FIG. 4 is an exploded perspective view illustrating a schematicconfiguration of a touch-panel-built-in liquid crystal display devicehaving a touch panel which is built in the liquid crystal display panel.

In FIG. 4, the reference sign “2” represents the TFT substrate, “3”represents the CF substrate, “21” represents the counter electrode (alsoreferred to as a common electrode), “5” represents the liquid crystaldriver IC, “MFPC” represents the main flexible wiring substrate, “40”represents a front window, and “53” represents the flexible wiringsubstrate for connection.

In the liquid crystal display device shown in FIG. 4, the back-sidetransparent conductive film (CD) on the CF substrate 3 is divided tohave a band-like pattern, and the detection electrodes (RX) 31 of thetouch panel are formed by the divided back-side transparent conductivefilm. The counter electrode 21 formed inside the TFT substrate 2 isdivided to have a band-like pattern, that is, divided into a pluralityof blocks, and also serves as scanning electrodes (TX) of the touchpanel. Because the detection electrode, (RX) and the scanning electrodes(TX) are formed in this manner, the touch panel substrate (41 of FIG. 1)is removed from the liquid crystal display device shown in FIG. 4.Hence, in the liquid crystal display device shown in FIG. 4, thefunction of the touch panel control IC (DRT) shown in FIG. 1 is providedin the liquid crystal driver IC5.

Next, referring to FIG. 5, the counter electrodes 21 and the detectionelectrodes 31 of the liquid crystal display device shown in FIG. 4 willbe described.

As described above, the counter electrodes 21 are provided on the TFTsubstrate 2. Plural (for example, about 20) counter electrodes 21 areconnected at both ends thereof in common, and are connected to a counterelectrode signal line 22.

In the liquid crystal display device shown in FIG. 5, the bundle-likecounter electrodes 21 also function as the scanning electrodes (TX).Accordingly, the counter electrode signal includes a counter voltageused in the image display and a touch panel scanning voltage used indetecting the touch position.

The detection electrodes 31 are disposed with a certain space relativeto the counter electrodes 21, and a capacitance is formed between eachdetection electrode 31 and each counter electrode 21. Accordingly, whenthe touch panel scanning voltage is applied to the counter electrode 21,a detection signal is generated in the detection electrode 31. Thedetection signal is extracted to the outside through a terminal 36 fordetection electrode.

In addition, dummy electrodes 33 are formed on both sides of eachdetection electrode 31. The detection electrodes 31 extend at one end,and form a detection electrode terminal 36 having a T shape. Further,not only the counter electrode signal line 22 but also various lines andterminals such as a driving circuit input terminal 25 and the like areformed on the TFT substrate 2.

FIG. 6 is a schematic cross-sectional view illustrating, in an enlargedmanner, a part of the cross section of a display section in the liquidcrystal display device shown in FIG. 4.

As shown in FIG. 6, a pixel section 200 is provided on the TFT substrate2, and each counter electrode 21 is used in the image display as a partof a pixel. Further, a liquid crystal composition 4 is sandwichedbetween the TFT substrate 2 and the CF substrate 3. As described above,a capacitance is formed between each detection electrode 31 provided onthe CF substrate 3 and each counter electrode 21 provided on the TFTsubstrate. Thus, when a driving signal is applied to the counterelectrode 21, the voltage of the detection electrode 31 is changed.

At this time, as shown in FIG. 6, if an electric conductor such as afinger 502 approaches or touches the front window 40, the capacitanceschange and the voltages generated in the detection electrodes 31 arechanged compared to the case where there is no approach or touch.

As described above, by detecting the changes in the capacitancesgenerated between the counter electrodes 21 and the detection electrodes31 formed on the liquid crystal display panel, a function of the touchpanel is provided in the liquid crystal display panel.

FIG. 7 is a top plan view illustrating an example of the counterelectrode divided into a plurality of blocks in the liquid crystaldisplay device according to an example of the invention. In FIG. 7, thereference sign “SUB1” represents the TFT substrate, “DRV” represents theliquid crystal driver IC, “CT1” to “CT20” represent the counterelectrodes of the blocks divided to have the band-like pattern, “DL”represents the video line, “CTL” represents a counter electrode line,“GES” represents a scanning line driving circuit which is built in theliquid crystal display panel, “GTL” represents a signal line forscanning line driving circuit, “TAM” represents a terminal portion whichis connected to the main flexible wiring substrate (MFPC), and “AR”represents a display section formed of a plurality of pixels arranged inmatrix.

The example shown in FIG. 7 employs a driving circuit, which has acircuit configuration using an a-Si single channel as the scanning linedriving circuit (GES), or a driving circuit which has a circuitconfiguration using a poly-Si single channel of which a semiconductorlayer is formed of an n-type polysilicon layer.

In the electrostatic capacitance type touch panel, in order to detectthe change in the electrostatic capacitance caused by a finger or thelike, it is preferable that the width of the scanning electrode (TX) forthe touch panel performing the AC driving be about 4 to 5 mm. Hence, asthe size of the liquid crystal display panel increases, the number ofscanning electrodes (TX) increases.

In the example shown in FIG. 7, the counter electrodes (CT) of 1280display lines are divided into 20 blocks (single block is formed of thecounter electrode of 64 display lines) formed of CT1 to CT20, and it isnecessary for 20 counter electrode lines (CTL) to be provided on each ofthe left and right sides.

The counter electrodes (CT1 to CT20) of the respective blocksdeteriorate image quality when voltages are changed by parasiticcapacitances in the display operation. Hence, it is necessary todecrease the resistance values of the counter electrode lines (CTL)which connect the liquid crystal driver IC (DRV) to the counterelectrodes (CT1 to CT20) of the respective blocks.

Further, since there are lines on the scanning line driving circuit(GES), the counter electrode lines (CTL) are not mounted on the scanningline driving circuit (GES). Hence, the counter electrode lines (CTL) aredisposed to be closer to the counter electrodes (CT) than the scanningline driving circuits (CES).

FIG. 8 is a top plan view illustrating a method of driving the counterelectrode divided into the plurality of blocks in the liquid crystaldisplay device according to another example of the invention.

The liquid crystal display device shown in FIG. 8 is different from theliquid crystal display device shown in FIG. 7 in that the counterelectrode selection circuits (CTSC), which select the respective counterelectrodes (CT1 to CT20) divided into 20 blocks through an addressdecoding method, are built in the liquid crystal display panel.

In FIG. 8, a driving circuit having a CMOS circuit configuration is usedas the counter electrode selection circuit (CTSC).

By adopting the address decoding method as the method of selecting thecounter electrodes (CT1 to CT20) divided into the 20 blocks, the lines,for which low resistances are necessary, are two lines of a line (LVcom)of a counter voltage (Vcom), which is supplied to the counter electrodes(CT1 to CT20), and a line (LVstc) of a touch panel scanning voltage(Vstc).

In the example, the touch panel scanning voltage (Vstc) is supplied as aDC voltage which is higher by 5 to 10V than the counter voltage (Vcom).The counter electrode selection circuit (CTSC) selects a scanninglocation on the basis of the address signal (addres) which is suppliedthrough an address signal line (Saddres), switches the counter voltage(Vcom) and the touch panel scanning voltage (Vstc) in response to thetouch panel scanning signal (STC), and outputs the counter voltage(Vcom) or the touch panel scanning voltage (Vstc) to the counterelectrode (CT) of the elected block which also serves as the scanningelectrode (TX).

In the liquid crystal display device shown in FIG. 8, even when thenumber of divisions of the counter electrode (CT) increases, only thenumber of the address signal lines (Saddres) increases. Therefore, in astate where the left and right frames of the liquid crystal displaypanel are prevented from being increased, it is possible to increase thenumber of divisions of the counter electrode used as the touch panelscanning electrodes.

FIG. 9 is a block diagram illustrating an exemplary configuration of thecounter electrode selection circuit (CTSC) shown in FIG. 8.

As shown in FIG. 9, the counter electrode selection circuit (CTSC)includes address decoder circuits (DEC1 to DEC20) and selection circuits(SCH1 to SCH20).

In the liquid crystal display device shown in FIG. 8, a single block isformed by electrically connecting the counter electrodes (CT), eachcorresponding to the 64 display lines, to one another in the liquidcrystal display panel such that the pitch of the scanning electrodes(TX) of the touch panel is 5 mm, whereby the 1280 display lines aredivided into 20. Then, the counter electrodes (CT1 to CT20) of the 20blocks correspond one-to-one with the address decoder circuits (DEC1 toDEC20). Since the number of divisions is 20 blocks, the address is 5bits, and 5 address signal lines (Sadd) are necessary.

The counter electrode of the single block selected by the address signal(addres), that is, the counter electrode (CT) corresponding to the 64display lines is AC-driven on the basis of the touch panel scanningsignal (STC), and the counter voltage is applied to the other counterelectrodes (CT).

FIG. 10 a circuit diagram illustrating an exemplary circuitconfiguration of selection circuits (SCH1 to SCH20) shown in FIG. 9.

In the selection circuit shown in FIG. 10, the output (DECO) of theaddress decoder circuit (DEC1 to DEC20) and the inverted signal of thetouch panel scanning signal (STC), which is inverted by an inverter(INV1), are input to a NOR circuit (NOR1). The selection circuit causesthe inverter (INV2) to invert the output of the corresponding NORcircuit (NOR1) and inputs the output to a switching circuit (SW),thereby selecting the touch panel scanning voltage (Vstc) or the countervoltage (Vcom) and outputting the voltage to the counter electrodes (CT1to CT20) of the respective blocks.

Thereby, when one of the address decoder circuits (DEC1 to DEC20) isselected, the touch panel scanning voltage (Vstc) and the countervoltage (Vcom) are switched in response to the touch panel scanningsignal (STC), and the voltage is output to the counter electrode of eachblock.

That is, in the selection circuit shown in FIG. 8, when the output(DECO) of the address decoder circuit (DEC1 to DEC20) is at the Lowlevel (hereinafter referred to as the L level) and the touch panelscanning signal (STC) is at the High level (hereinafter referred to asthe H level), the output of the NOR circuit (NOR1) is at the H level,and therefore the switching circuit (SW) selects the touch panelscanning voltage (Vstc). In contrast, when the touch panel scanningsignal (STC) is at the L level or the output (DECO) of the addressdecoder circuit (DEC1 to DEC20) is at the H level, the output of the NORcircuit (NOR1) is at the L level, and therefore the switching circuit(SW) selects the counter voltage (Vcom).

FIG. 11 is a circuit diagram illustrating an exemplary circuitconfiguration of the address decoder circuit (DEC1 to DEC20) shown inFIG. 9.

As shown in FIG. 11, in the address decoder circuit (DEC1 to DEC20), theaddress signal as it is or the inverted signal, which is generated byinverting the address signal through the inverter (INV), is input toeach of the 5 address signals (addres), and decoding is performed on thebasis of the combination of the H and L levels of the 5 address signals(addres).

In the address decoder circuit shown in FIG. 11, the address signal(add), which is a predetermined combination of the 5 address signals(addres), is input to NAND circuits (NAND1, NAND2), and the outputs ofthe corresponding NAND circuits (NAND1, NAND2) are input to a NORcircuit (NOR2). Then, the output of the corresponding NOR circuit (NOR2)is inverted by the inverter (INV3), and becomes the output (DECO) of theaddress decoder circuit. Accordingly, the address decoder circuit shownin FIG. 11 outputs the voltage with the L level as the output (DECO)when the combination of the address signals coincides with thecombination of the address signals set by the address decoder circuititself, and outputs the voltage with the H level as the output (DECO)when the combination of the address signals does not coincide with thecombination of the address signals set by the address decoder circuititself.

FIG. 12 is a diagram illustrating a driving waveform at the time ofpixel writing and at the time of touch position detection on the touchpanel in the touch-panel-built-in liquid crystal display device.

In FIG. 12, the signal waveform A indicates a pulse waveform of thetouch panel scanning voltage (Vstc) which appears in the output voltageof the selection circuit (SCH11) supplied to the counter electrode(CT11) of the 641 to 704 display lines of the 11th block among thecounter electrodes divided into the 20 blocks. Further, the signalwaveform B indicates a waveform of a video voltage supplied to the videolines (DL) of the odd columns. The signal waveform C indicates awaveform of a video voltage supplied to the video lines (DL) of the evencolumns. The signal waveform D indicates a pulse waveform of the gatesignal (selection scanning voltage) which is supplied to the gateelectrode of the thin film transistor at the 641st display line throughthe 641st scanning line (GL). Furthermore, the time period T1 indicatesa touch position detection time period, and the time period T2 indicatesa pixel writing time period.

The touch position detection time period (T1) is set as a time periodother than the pixel writing time period (T2) in order to prevent theeffect to the display. Further, in the touch position detection timeperiod (T1), in order to increase the detection sensitivity, scanning isperformed plural times by the scanning electrode (TX) at the samelocation. Specifically, in FIG. 12, the counter electrode (CT11) of the11th block is supplied with the touch panel scanning voltage (Vstc)plural times. Further, in the pixel writing time period (T2), thecounter electrode (CT11) of the 11th block is not supplied with thetouch panel scanning voltage (Vstc), but supplied with the countervoltage (Vcom).

FIG. 13 is a diagram illustrating the timing of the pixel writing andthe timing of the touch position detection on the touch panel in thetouch-panel-built-in liquid crystal display device.

In FIG. 13, the reference sign “A” indicates the timing of pixel writingfrom the 1st display line to the 1280th display line in the pixelwriting time period (T4) of the single frame, and the reference sign “B”indicates the timing of detecting the touch position on the touch panelin the counter electrodes (CT1 to CT20) of the respective blocks dividedinto the 20 blocks.

As shown in FIG. 13, by causing the counter electrode of an arbitrarydisplay line to function as the scanning electrode (TX), the scanningoperation at the time of touch position detection is performed at alocation different from that of the gate scanning which performs pixelwriting. It should be noted that, in FIG. 13, the reference sign “T3”represents a flyback period, “VSYNC” represents a verticalsynchronization signal, and “HSYNC” represents a horizontalsynchronization signal.

FIG. 14 is a diagram illustrating a circuit configuration of the liquidcrystal driver IC (DRV) according to an example of the invention.

As shown in FIG. 14, in the liquid crystal driver IC (DRV) according tothe example, various circuits for driving the liquid crystal displaypanel are mounted on the same semiconductor chip. Specifically, theliquid crystal driver IC has the following built-in components: acontrol circuit 101 for the scanning line driving circuit (GES); asource amplifier circuit 102; a gradation voltage generation circuit103; a VGH/VGL generation circuit 108; a VSP/VSN generation circuit 107;a TX control circuit 104; a common amplifier circuit 105; and a RXdetection circuit 106. The liquid crystal driver IC5 and the scanningline driving circuit (GES) constitute a driving circuit for both of aliquid crystal display function and a touch panel function in the liquidcrystal display panel. It should be noted that the TX control circuit104 is a circuit, which is hitherto mounted on the exclusivesemiconductor chip, for the touch panel control function. Further, inFIG. 14, the reference numbers “109” and “110” represent externalcomponents.

Then, in order to optimize the circuit size of the semiconductor chip,the power supply of the TX control circuit 104, the common amplifiercircuit 105, and the RX detection circuit 106 is configured such thatthe voltages of various voltage generation circuits for driving theliquid crystal display panel are shared.

FIGS. 15A and 15B show voltage signals used in driving the liquidcrystal in the liquid crystal display device according to the example.FIG. 15A shows liquid crystal driving voltages at the time of normaldisplay. FIG. 15B shows liquid crystal driving voltages at the time of“black” display.

In FIGS. 15A and 15B, VGH is a voltage which is supplied to the scanningline of the liquid crystal display panel in order to turn on the thinfilm transistors (TFT) of pixels, and VGL is a voltage which is suppliedto the scanning line of the liquid crystal display panel in order toturn off the thin film transistors (TFT) of pixels.

VDL is a video voltage which is output from the source amplifier circuit102 and is supplied to the video line (DL) of the liquid crystal displaypanel.

Vcom is a counter voltage which is supplied to the counter electrodes(CT). In the liquid crystal display device according to the example, thedot inversion driving method and the column inversion driving method areadopted as the AC driving method. Hence, the counter voltage (Vcom),which is supplied to the counter electrodes (CT), is a constant voltagein the time period other than that of the scanning operation at the timeof touch position detection.

Vstc is a touch panel scanning voltage which is supplied to the selectedcounter electrodes (CT) in the time period of the scanning operation atthe time of touch position detection.

VSP and VSN are power supply voltages of the source amplifier circuit102, and are voltages necessary for generating the output voltage of thesource amplifier circuit 102.

As described above, in the scanning operation at the time of touchposition detection on the touch panel, the counter electrodes (CT)function as the scanning electrodes (TX) at a location different fromthat of the gate scanning for performing pixel writing, and the touchpanel scanning voltage (Vstc) is supplied to the counter electrodes(CT). Then, by detecting the changes in the detection voltage detectedthrough the detection electrodes (RX) in the RX detection circuit 106 insynchronization with the timing of the scanning operation, the touchpanel function is implemented.

The liquid crystal driving voltages at the time of “black” display shownin FIG. 15B are the same as the voltages in FIG. 15A other than thevideo voltage (VDL) which is output from the source amplifier circuit102. However, the voltage difference between the common voltage (Vcom)and the video voltage at the time of “black” display is minimized.

FIG. 16 is a diagram illustrating an electrode shape of the touch panelof the liquid crystal display device according to the example.

The scanning electrodes (TXn) of FIG. 16 correspond to the dividedcounter electrodes (CT1 to CT20) shown in FIGS. 7 and 8, and thedetection electrodes (RXn) correspond to the detection electrodes 31shown in FIG. 4.

FIG. 18 is a system state transition diagram of the liquid crystaldisplay device according to the example.

At the time of the normal operation shown in FIG. 18, a normal image isdisplayed on the liquid crystal display panel, and the liquid crystaldisplay panel is driven on the basis of the voltage relation shown inFIG. 15A.

Further, at the time of the normal operation, as shown in FIG. 17A, thetouch panel scanning voltage (Vstc) is output for each frame (FLM),whereby the scanning operation for detecting the touch position on thetouch panel is performed. In such a manner, the touch panel function isoperated all the time.

As shown in FIG. 18, in a standby state of register setting made fromthe host, the “black” image is displayed on the liquid crystal displaypanel. Further, the standby state, as shown in FIG. 17B, the touch panelscanning voltage (Vstc) is not supplied for each frame, but is thinnedout to be output to plural frames (FLM) once, whereby the scanningoperation for detecting the touch position on the touch panel isperformed. In such a manner, power consumption is reduced.

When the touch panel and the liquid crystal display panel are controlledby an individual semiconductor chip, the “black” display is non-display(not operated), and the electric power ideally reaches 0.

However, in the system configuration of the example, the voltage for thetouch panel function and the driving voltage for display are generatedas a common voltage. Hence, in order to operate the touch panel functioneven in the “black” display in the standby state, it is necessary tooperate various voltage generation circuits for driving the liquidcrystal display device.

Therefore, in the liquid crystal driver IC (DRV) of the example, powerconsumption of “black” display is reduced, and thus low powerconsumption is achieved by the combination of adjustment and stop ofvarious voltage generation circuits to be described later.

FIG. 19 shows a circuit configuration of the source amplifier circuit102 according to the example.

As shown in FIG. 19, in the source amplifier circuit 102 of the example,the amplifier circuit (voltage follower circuit; AMPD) is connected to acurrent adjustment circuit (VDIo) which has a function capable ofadjusting current through the register setting. In the standby state,the source amplifier circuit 102 lowers current, which is output fromthe current adjustment circuit (VDIo), compared with the normaloperation, and reduces the current which flows in the amplifier circuit(AMPD), thereby achieving low power consumption. Further, the currentadjustment circuit (VDIo) may be deactivated. At the time of theinactivation, a ground voltage (GND) is output by a switching circuit(SWD).

FIG. 20 shows a circuit configuration of the common amplifier circuit105 according to the example.

As shown in FIG. 20, in the common amplifier circuit 105 of the example,the amplifier circuit (voltage follower circuit; AMPC) is connected to acurrent adjustment circuit (VCIo) which has a function capable ofadjusting current through the register setting. In the standby state,the common amplifier circuit 105 lowers current, which is output fromthe current adjustment circuit (VCIo), compared with the normaloperation, and reduces the current which flows in the amplifier circuit(AMPC), thereby achieving low power consumption. Further, the currentadjustment circuit (VCIo) may be deactivated. At the time of theinactivation, a ground voltage (GND) is output by a switching circuit(SWC).

FIG. 21 shows a circuit configuration of the gradation voltagegeneration circuit 103 according to the example. It should be noted thatFIG. 21 shows only the gradation voltage generation circuit whichgenerates positive gradation voltages, but in practice, there is alsoprovided a gradation voltage generation circuit which generates negativegradation voltages.

As shown in FIG. 21, the gradation voltage generation circuit 103according to the example has gradation voltage generation resistances(VR) of which the resistance values are variable in the registersetting, in which amplifier circuits (AMPR1 to AMPR3) are disposed atthe output points of the gradation voltages (video voltages) applied tothe liquid crystal in the gradation voltage generation resistances (VR).

The amplifier circuits (AMPR1 to AMPR3) are connected to the currentadjustment circuit (VR1Io to VR3Io) each of which has a function capableof adjusting current through the register setting. In the standby state,the gradation voltage generation circuit 103 lowers current, which isoutput from each current adjustment circuit (VR1Io to VR3Io), comparedwith the normal operation, and reduces the current which flows in eachamplifier circuit (AMPR1 to AMPR3), thereby achieving low powerconsumption. Further, each current adjustment circuit (VR1Io to VR3Io)may be deactivated. At the time of the inactivation, a ground voltage(GND) is output by each switching circuit (SWR1 to SWR3).

FIG. 22 shows a circuit configuration of a VGH/VGL generation circuit108 according to the example.

The VGH/VGL generation circuit 108 shown in FIG. 22 is acharge-pump-type step-up circuit using only capacitors (C1 to C3) asexternal circuits (external circuits 109 of FIG. 14). The VGH/VGLgeneration circuit 108 has a switching circuit (SW1) and a switchingcircuit (SW2) which switch connections of the plural capacitors (C1 toC3), and generates high voltages from the low voltage of about 3V whichis input from the outside by alternately switching the switching circuit(SW1) and the switching circuit (SW2).

The circuit shown in FIG. 22 has a configuration for generating acertain 1-level voltage. When generating voltages with plural levels,plural circuits shown in FIG. 22 are provided.

The adjustment circuit 121 provided in the VGH/VGL generation circuit108 is able to adjust switching periods of the switching circuit (SW1)and the switching circuit (SW2) in accordance with the register setting,whereby the VGH/VGL generation circuit 108 is able to adjust the currentsupply capability.

FIG. 23 shows a circuit configuration of the VSP/VSN generation circuit107 according to the example.

The circuit is a circuit used in the voltage generation circuit thatgenerates about 6V which the current supply capability of the circuitconfiguration of FIG. 22 is not enough to supply.

In FIG. 23, in the example of the circuit configuration that generatesonly the VSP voltage, one set of the same circuit configuration isadditionally necessary at the time of VSN voltage generation.

The external circuit 110 includes, as shown in FIG. 23, an inductor (L),a Schottky barrier diode (D), a capacitor (C), and a MOS transistor(TR). The gate on/off control of the MOS transistor (TR) is performed bythe PWM generation circuit 131. The PWM generation circuit 131 fixes thefrequency of the gate pulse, and controls the high width and the lowwidth of the gate pulse. The VSP/VSN generation circuit 107 has abuilt-in period adjustment circuit 132 capable of adjusting thefrequency of the gate pulse in accordance with the register setting.

In the circuit of FIG. 23, the energy of the inductor (L) generated bythe switching of the MOS transistor (TR) is rectified by the Schottkybarrier diode (D), whereby it is possible to obtain a constant voltage.The capacitor (C) holds the constant voltage, and uses the voltage,which is held in the capacitor, as a VSP voltage.

The voltage comparator circuit 133 compares the VSP voltage, which isheld in the capacitor (C), with a reference voltage set as a targetvoltage, and the PWM generation circuit 131 keeps the VSP voltageconstant by controlling the high width and the low width of the pulse inaccordance with the comparison result.

FIG. 24 shows combinations of various kinds of adjustment circuit statesfor achieving lower power consumption in the standby state in the liquidcrystal display device according to the example.

First, at the time of the normal operation shown in FIG. 18, the liquidcrystal display device is driven by the dot inversion driving method orthe like, and displays the normal image on the liquid crystal displaypanel. At that time, it is necessary for the liquid crystal displaydevice to be driven by using the liquid crystal driving voltages shownin FIG. 15A. Hence, the current capabilities of various voltagegeneration circuits are optimized such that the electric power isminimized, but are set on the basis of a normal specification which isnot extremely limited.

Meanwhile, the liquid crystal display device may be in the display offstate, in which “black” is displayed on the liquid crystal displaypanel, as the standby state shown in FIG. 18. In this case, as shown inFIG. 15B, the video voltage (VDL), which is output from the sourceamplifier circuit 102, has no potential difference from the commonvoltage (Vcom), in which current is unlikely to be charged or dischargedto the liquid crystal. Accordingly, the low power consumption isachieved in accordance with the situation.

First, in the low power consumption mode 1, the AC driving method of theliquid crystal panel is changed from the dot inversion driving methodinto a column inversion driving method (or an inversion driving methodfor each column), whereby the charged or discharged current is reducedto be applied once in a single frame in the liquid crystal.

At this time, only “black” is displayed on the liquid crystal displaypanel. Hence, in the gradation voltage generation circuit 103, it isenough to operate a minimum necessary number of amplifier circuits.Accordingly, only the amplifier circuits of approximately 6V and the GNDvoltage, that is, a top amplifier circuit (AMPR1), which is an amplifiercircuit outputting the highest gradation voltage, and a bottom amplifiercircuit (AMPR3), which is an amplifier circuit outputting the lowestgradation voltage, are operated, and the middle amplifier circuit, whichis an amplifier circuit of the middle voltage other than those, isdeactivated, thereby achieving low power consumption.

Next, the low power consumption mode 2 will be described. In the standbystate, the charged or discharged current necessary for the sourceamplifier circuit 102 is small. Hence, it is possible to reduce thecurrent capability of VSP/VSN as the power supply voltage of the sourceamplifier circuit 102. Accordingly, in the low power consumption mode 2,in addition to the above-mentioned setting made in the low powerconsumption mode 1, the pulse period of the PWM generation circuit 131of the VSP/VSN generation circuit 107 is set to be increased by theperiod adjustment circuit 132, and the current capability is set to below, thereby achieving low power consumption.

Further, in addition to this, the amounts of currents in the sourceamplifier circuit 102 and only the two active amplifier circuits (AMPR1,AMPR3) of the gradation voltage generation circuit 103 are adjusted tobe minimized, thereby achieving low power consumption.

In the low power consumption mode 3, in addition to the setting of thelow power consumption mode 2, the gate scanning of the liquid crystaldisplay panel is thinned out for each one frame to be performed once inn frames, the electric power of the scanning line driving circuit (GES)is reduced, and the switching periods of the switching circuit (SW1) andthe switching circuit (SW2) are set to be increased by the adjustmentcircuit 121 of the VGH/VGL generation circuit 108, thereby achievingfurther low power consumption.

In the low power consumption mode 4, in addition to the setting of thelow power consumption mode 3, by deactivating the source amplifiercircuit 102 and the amplifier circuits of the gradation voltagegeneration circuit 103, the outputs of the amplifier circuits are set tothe GND voltage by the switching circuits (SWD, SWR3). Furthermore, byalso deactivating the common amplifier circuit 105, the output of thecommon amplifier circuit 105 is set to the GND voltage.

Thereby, the negative voltage applied to pixels is eliminated, and thusthe VSN generation circuit becomes inactive, whereby the current isreduced. The VSP generation circuit remains active since it is necessaryto output the touch panel scanning voltage (Vstc) at the time of thetouch position detection.

With such combinations, low power consumption is achieved in theintegral driver IC which performs the touch panel driving and the liquidcrystal driving. It should be noted that the combinations of FIG. 24 areexamples and low power consumption can be achieved in othercombinations.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A liquid crystal display device comprising: aliquid crystal display panel that has a first substrate, a secondsubstrate, and a liquid crystal sandwiched between the first substrateand the second substrate; a plurality of pixels formed in a displaysection of the first substrate; a plurality of pixel electrodes formedin the pixels respectively; a plurality of pixel transistorselectrically connecting with the plurality of pixel electrodesrespectively; a plurality of common electrodes respectively formed asfacing to the pixel electrodes, formed in the first substrate, and usedfor detection of a conductor approaching or touching; and a drivingcircuit supplying a common voltage for displaying an image to the commonelectrodes and a scanning voltage for detecting the conductor to thecommon electrodes, wherein the display device has a first mode fordisplaying an image in the display section and a second mode that is astandby mode, wherein the first mode has a first period for displayingan image and a second period for detecting, wherein the second mode hasa third period in which the display section is in a standby state and afourth period for detecting, wherein the display panel detects theconductor by using the common electrodes in the second period and thefourth period, wherein the pixel transistor supplies an image signal tothe pixel electrodes in the third period, and does not supply the imagesignal to the pixel electrodes in the fourth period, and wherein anoutputting rate of the scanning voltage in the fourth period is lowerthan that in the second period.
 2. The liquid crystal display deviceaccording to claim 1, wherein a voltage difference between the commonvoltage and the image signal which is supplied to the pixel electrode inthe third period is minimized.
 3. The liquid crystal display deviceaccording to claim 1, wherein power consumed for detecting the conductorin the second mode is lower than power consumed for detecting theconductor in the first mode.
 4. The liquid crystal display deviceaccording to claim 1, wherein scanning operations are performed forsequentially supplying the scanning voltage to the common electrodes inthe second period and the fourth period.
 5. The liquid crystal displaydevice according to claim 1 further comprising: a voltage generationcircuit, wherein a voltage which is generated by the voltage generationcircuit in the second mode is lower than a voltage which is generated inthe first mode.
 6. The liquid crystal display device according to claim1, wherein a state of the pixel transistor is OFF state in the fourthperiod.
 7. The liquid crystal display device according to claim 1,wherein the first mode is normal operation mode and the second mode isthe standby mode.
 8. The liquid crystal display device according toclaim 1, wherein color of the display section is black in the thirdperiod.
 9. A liquid crystal display device comprising: a liquid crystaldisplay panel that has a first substrate, a second substrate, and aliquid crystal sandwiched between the first substrate and the secondsubstrate; a plurality of pixels formed in a display section of thefirst substrate; a plurality of pixel electrodes formed in the pixelsrespectively; a plurality of pixel transistors electrically connectingwith the plurality of pixel electrodes respectively; a plurality ofcommon electrodes respectively formed as facing to the pixel electrodes,formed in the first substrate, and used for detection of a conductorapproaching or touching and a driving circuit supplying a common voltagefor displaying an image to the common electrodes and a scanning voltagefor detecting the conductor to the common electrodes, wherein thedisplay device has a first mode for displaying an image in the displaysection and a second mode that is a standby mode, wherein the first modehas a first period for displaying an image and a second period fordetecting, wherein the second mode has a third period in which thedisplay section is in a standby state and a fourth period for detecting,wherein the display panel detects the conductor by using the commonelectrodes in the second period and the fourth period, wherein the pixeltransistor is ON state for supplying an image signal to the pixelelectrodes in the third period, and is OFF state in the fourth period,and wherein a number of outputting the scanning voltage in the fourthperiod is lower than that in the second period.
 10. The liquid crystaldisplay device according to claim 9, wherein a voltage differencebetween the common voltage and the image signal which is supplied to thepixel electrode in the third period is minimized.
 11. The liquid crystaldisplay device according to claim 9, wherein power consumed fordetecting the conductor in the second mode is lower than power consumedfor detecting the conductor in the first mode.
 12. The liquid crystaldisplay device according to claim 9, wherein scanning operations areperformed for sequentially supplying the scanning voltage to the commonelectrodes in the second period and the fourth period.
 13. The liquidcrystal display device according to claim 9 further comprising: avoltage generation circuit, wherein a voltage which is generated by thevoltage generation circuit in the second mode is lower than a voltagewhich is generated in the first mode.
 14. The liquid crystal displaydevice according to claim 9, wherein the first mode is normal operationmode and the second mode is the standby mode.
 15. The liquid crystaldisplay device according to claim 9, wherein color of the displaysection is black in the third period.